C15orf2 (Chromosome 15 open reading frame 2) is an intronless gene, which is located in the Prader-Willi syndrome (PWS) chromosomal region on human chromosome 15. Mice do not have an orthologous gene. Here we show that expression of C15orf2 in the fetal human brain is imprinted. Using Western blot and immunohistological studies we have obtained evidence that C15orf2 protein is present in several regions of the brain. Previously published phylogenetic studies as well as population genetic studies based on complex haplotypes as described here suggest that C15orf2 is under positive Darwinian selection. These results indicate that C15orf2 might have an important role in human biology and that a deficiency of C15orf2 might contribute to PWS.